crack in weld problem

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A potential new customer is having problems with their welding source in that many welds are cracking, and evidently there not willing to search out the exact reason why. Material is 3/8" 1018 CRS rod with a small plate tacked on about 4" in from each end. The plate is a stamping say 1/8" x 1 x 1 1/2" 1010 CRS. The plate is case hardened to 50 Rockwell & then Nickel plated before welding, now approximately 15% will develop a crack right threw the center of weld. I don't know what filler or process the other guy is using, yet it seems that no heat is involved and I assume he's using mild steel. What filler would work best? I would think that ones fighting the fact its case hardened. Maybe a 312 rod. Any thoughts appreciated.J P Streets Welding LLC
Reply:why is  it plated before the welding????  gota  remove the plate to get to the base metal
Reply:i m guessing  maybe  shouldn t plating b done b 4 the weld
Reply:Well without more info folks are stuck with just throwing darts at what the problem could be. Could be it's nothing more than the simplest form of 'hot cracking'. Not enough heat went into the base metal to provide sustained heat and the tack is left to cool quickly with just enough fusion to hold it's edges in place. It's gonna crack a good portion of the time. If a tack is going to need to provide decent holding power for an interim period I always check them for cracks just because of that. I also grind all my tacks out before weldin up a tacked section. Nickel plated or not there's going to have to be some heat put into them if you want them to hold. Especially if you're going to tack one side then tack the other side. The shrinkage is working against each other. I think everybody here has heard a tack pop before, "pink".
Reply:When that mild steel is case hardened, depending on the depth of the treatment, a high level of carbon has been absorbed anywhere from .02 to maybe .05 thickness.  When you consider that, most of the material has a very high carbon content.  High carbon steel is subject to cracking when welded.
Reply:As for now I don't know the wire used by the welding outfit that is doing the job now. I have seen parts with welds cracked through the center.Yes the 50 rockwell case hardened parts is one issue!Also the nickel plated is another!Next week I should have some parts to R & D on. I'm curious to how well silicon bronze  or 312 stl. st or 888 will hold up, 312 & 888 weldmold have good elasticity properties whereby silicon bronze may be a better answer for its more like brazing.J P Streets Welding LLC
Reply:These plates are tacked to 1/2" CRS octogon shaft about 18" long, 2 plates tacked together in center of shaft, the other 2 plates are tacked 1 on each end of shaft in say 3". These serve as a guide to feed part into robotic machine for the covering of plastic or rubber molding which does not cover the plates and maybe thats why there plated.J P Streets Welding LLC
Reply:We have a project where I work at that calls for a bracket to be nickel plated and then welded. The weld develops cracks all the time, we finally ended up sanding the plating off the bracket where we are to weld it, than make the weld. helps alot, but in some cases it still develops cracks. Material is the same 1010-1018 steel and we are TIG welding it with ER70S-2 filler
Reply:Try doing it with a stainless steel 309L filler or maybe even a 310/310Cb.  The stainless rods might cooperate with the nickel plating a little better.
Reply:Jerry,was this question posted on another forum, I responded to this before?  Do a web search on "nickel plating phosphorus" and you'll find that some nickel plating processes use up around 12% phosphorus.  Phosphorus is an undesireable impurity in steels and is well known to cause "hot cracking" such as is generally indicated by a "center-line" crack.I suppose you could calculate the carbon addition to the weld from the case hardened component, but I don't believe center-line cracking is generally associated with a hardened weld metal, I think it may tend to be more along the fusion line of the weld.
Reply:Yes Pulser I posted this on maybe 5 forums, which to me is in front of  thousands of welding related folks. I have since found that the cracking is occuring at the base also. As for removing the plating I don't feel that would be best way to go, time consuming etc..Ran some samples and here's what I found.Tig filler Pre heat Hammer test1) ER70S-2 NO Broke easily2) Sil Bronze NO Broke but was better3) 312 Stl. st. NO Broke but was better then both4) 312 Stl. st 150 degrees Weld held, cracked base metal 5) ER70S-2 150 Same as aboveSmall pre heat seemed to give good weld and after hammering part back and forth actually started cracking the plated base metalJ P Streets Welding LLC
Reply:Jerry, it doesn't sound like this is a high stress part, so have you considered a low temperature solution?  (something like furnace brazing rod or silver solder...)
Reply:Nickel silver brazed joins are just as strong as welded joints at 70ksi.  They can even be stronger because they wet out and spread into all of the gaps.